Caused by being pregnant with the baby due but not giving birth that morning.

Walking around causes contractions.

After walking around too much the baby will be born anyway, right there on the spot.

Walking in front of the fountain in Hot Spring Town or the main road in the Capital will automatically trigger birth. Workaround: If you want to reach the Clinic before birth, pay the guide to go to Industrial District and approach the Clinic from the north (or try to circumvent the city and enter by the Slum Back Gate and, once again, cross the main street from the north).